Field of the Invention
Embodiments described herein generally relate to controlling the velocity of a gas flowing to a combustion chamber.
Description of the Related Art
Many industrial operations employ furnaces within which fuel and oxidant are combusted, so that the heat of combustion can heat material that is in the furnace. Examples include furnaces that heat solid material to melt it, such as smelting furnaces, and furnaces that heat objects such as steel slabs to raise the material's temperature (short of melting it) to facilitate shaping or other treatment of the material or object. The required high temperature is generally obtained by combustion of a hydrocarbon fuel such as natural gas. The combustion produces gaseous combustion products, also known as flue gas. Especially glass melting furnaces that achieve a relatively high efficiency of heat transfer from the combustion to the solid materials to be melted, the flue gases released generally reach temperatures in excess of 1300 degrees Celsius (° C.), and thus represent a considerable waste of energy that is generated in the high temperature operations, unless that heat energy can be at least partially recovered from the combustion products.
One mechanism to recover this lost energy is to preheat one or more of the combustion reactants (fuel or oxidant) using the flue gases. The combustion reactants can be heated to a desired temperature, thus increasing the heat delivered to the furnace during the combustion process. However, problems arise from the preheating of the combustion reactants. As the combustion reactants are heated in a given space, the pressure of the gases increases thereby leading to an increase in jet velocity exiting the burner. Jet velocity is the velocity with which the gases escape the burner. Increased jet velocity leads to shorter residence time before the combustion reaction which can reduce flame luminosity. A larger jet using a larger diameter of a pipe can resolve this problem, but this solution only creates a new problem when a lower reactant temperature is used. In other words, the velocity of the reactant decreases at the lower temperature in comparison to that of the reactant at the higher reactant temperatures.
Another way to overcome this problem is to use one pipe for the standard temperature fuel and another pipe for the hot fuel, with a valve switching the fuel flow between the two pipes. However, conventional valve designs used in the combustion art are complex devices that do not work well, or sometimes at all, at elevated temperatures. Further, conventional valves require manual operation (i.e. a person operating the valve based on temperature) which would require insulation and extra protection equipment for the operator. Also, insulating the valve requires even greater complexity and expense in order to ensure that the valve can perform in a routine fashion. Therefore, it is desirable for burners to have a function of automatic adjustment to maintain the proper jet velocity irrespective of the temperature change of the gas.
Thus, there is a need in the art for control of gas velocity exiting the burner during burner operations based on temperature.